(a). Field of the Invention
The invention relates to communication systems, and more particularly to an apparatus and method for selecting antennas in a MIMO (i.e. Multiple Input Multiple Output) multi-carrier system.
(b). Description of the Prior Arts
In modern communication systems, the MIMO technology is often used in order to achieve a higher transmission rate and a wider transmission range. The MIMO technology employs multiple transmit antennas and multiple receive antennas to transmit multiple mutually independent signal streams simultaneously. Though the MIMO technology may enhance the system performance, the use of multiple receive antennas also increases the power consumption of the receiver of the system. Therefore, it becomes essential for the system to efficiently select receive antennas that work better for signal detection among all the receive antennas, so as to reduce the power consumption. When only one signal stream is transmitted at one time, receive antennas that have the strongest signal energy may be selected as sources of received signals, so as to perform signal detection. However, when multiple signal streams are transmitted simultaneously, to select the receive antennas based on the strength of received signal cannot have a significant benefit due to the fact that the signal streams interfere with each other.
For a multi-carrier system such as an OFDM (i.e. Orthogonal Frequency Division Multiplexing) system, since signals are transmitted on multiple sub-carriers simultaneously, the interference between multiple signal streams is rendered more complicated when the MIMO technology is utilized. Consequently, if receive antennas that have the strongest signal energy are directly selected for performing signal detection, the benefit is even less significant.